This invention pertains to the art of ultraviolet germicidal lamps used for air sterilization.
The invention is applicable to compact ultraviolet germicidal sterilization units which are inserted within the air ducts of forced air heating and cooling systems, and will be described with particular reference thereto. It will be appreciated, however, that the invention has broader applications and may be advantageously employed in other environments and applications that benefit from the sterilization of recirculated air.
Ultraviolet energy which can be grouped into three wavelength categories, "long," "middle," and "short" wave ultraviolet, has been shown to be beneficial for a variety of uses. All of ultraviolet wavelengths are shorter than visible light waves and, therefore, are invisible to the human eye.
It has been further shown that ultraviolet wavelengths in the short wave category, and in particular in the region of 253.7 nm, are useful in the destruction of bacteria and other micro-organisms in the air or on exposed surfaces. Micro-organisms which are invisible to the unaided eye, include bacteria, mold spores, yeast and viruses. Each of these are microbes, but different from each other. Microbes are living cells approximately 1/25,000 of an inch in length which reproduce by one cell dividing every twenty minutes or faster. This is a continuous cycle and, if left unchecked, from one bacteria there would be several billion bacteria in less than twelve hours. Indoor air may contain countless bacteria and mold spores and/or viruses, which are the source of spoilage of perishable products and the cause of disease in humans and animals. Germicidal rays emitted by ultraviolet lamps in the short wavelengths in the range of 253.7 nm travel through the air and destroy micro-organisms which are in the path of the rays.
In order for the ultraviolet rays to kill bacteria, etc., the rays must directly strike the micro-organisms. Thus, micro-organisms floating in the air may easily be reached by the ultraviolet rays and, therefore, are readily destroyed. Exposure to ultraviolet rays necessary to kill bacteria, etc. is the product of time and intensity. High intensity for a short period of time, or low intensity for a long period are fundamentally equal in lethal action on bacteria (disregarding the life cycle of the bacteria).
It has been found that the characteristics of germicidal ultraviolet, i.e. those rays in the short wavelength region of 253.7 nm, are useful in air heating and cooling systems to make the air passing through system ducts equivalent, as much as possible, to outdoor air in freedom from live bacteria, etc.
In the average installation, a 90% kill of air borne bacteria, equivalent to most outside air, is recommended. Where a maximum sterilization is imperative, as in hospitals and pharmaceutical laboratories, the highest bacterial reduction possible is desirable--at least 98%. Such conditions can be obtained by increasing the number of lamps in the air conditioning system.
Since the effectiveness of their radiation increases with time of exposure, ultraviolet (germicidal) are known to be installed in the part of the heating and cooling system where the air velocity is the lowest. It has been determined that placement after the filters, if at all possible, is optimal.
A specific example of existing ultraviolet sterilization equipment inserted within forced air heating and cooling system A is illustrated in FIG. 1. Sterilization equipment B is located at an intake end of cool air return duct D, and sterilization equipment C is located in a centralized area of cool air return duct D. A preferred location for placement of sterilization equipment C is within the cool air return D. While ultraviolet lamps can be placed on the warm air side of the system, this tends to decrease the life of the ultraviolet lamps. As can be seen more closely in FIGS. 2a-2c, such lamps are presently arranged in a variety of configurations, including FIG. 2a which is a lamp holder E with one lamp F, FIG. 2b a lamp holder G with two lamps H, I as well as FIG. 2c which is a sixteen lamp grid J arrangement four feet square by eighteen inches deep. Thus, existing units may be used in a small installations such as found in homes, as well as in larger industrial type heating/air conditioning systems found in commercial buildings.
A drawback known to exist in using germicidal ultraviolet lamps for sterilizing recirculating air is that the rays from ultraviolet lamps are harmful to the eyes and skin of humans and animals.
For this reason, in personal protection applications, that is, the use of the lamps for room irradiation in homes, schools, offices, etc., indirect fixtures are placed on the wall or suspended from the ceiling above eye level. Only the upper air is irradiated and the people occupying the room should receive no direct radiation. It is also known that plant life may be damaged by direct or reflected germicidal ultraviolet rays and transient dyes and colors will fade from exposure to ultraviolet rays.
When sterilization equipment such as B and C are within the forced air heating and cooling system A, there is no concern as to harm to humans, animals, plants, etc. However, over time the lamps degrade and need to be replaced. Also, it is important that functioning lamps be kept on a maintenance schedule which includes cleaning and inspection. Dust in the air within air ducts tend to cover the lamps, thereby degrading their usefulness by limiting the intensity and amount of ultraviolet rays emitted. Cleaning, inspection and replacement of lamps require complete removal of equipment B and C from heating and cooling system A.
A concern with removal of such sterilization equipment is the possibility of harm being caused due to the lamps being removed while they are energized. Manufacturers of these units address the issue of safety by requiring large "Caution" notices and other warnings near the lamp fixtures instructing a person to ensure that they de-energize the lamps prior to working near the installation. The commonly suggested warning is that no one should look directly at a lighted lamp, or work near a lighted lamp without adequate eye protection. It is further suggested that tube and reflector cleaning and tube replacement should be entrusted only to personnel who will observe the strict precaution of never exposing the face and eyes to a lighted tube while they are working on it or on the reflector. It is noted that reflectors are often used to direct the rays of the lamps in installations.
In larger units such as the sixteen lamp configuration J shown in FIG. 2e, it is possible to provide an access door for periodic checking and cleaning of the lamps in a chamber or air duct in which the lamps are mounted. As a safety measure, some installations configure the door so it is locked with an electrical circuit such that the lamps are turned off automatically when the door is open. Further, a window of ordinary glass, which filters out the ultraviolet, is provided to allow safe observation of the lamps.
Thus, as illustrated in FIGS. 1 and 2, for small size installations, such as household use, etc. the manner of ensuring that harmful rays are not viewed by a user replacing or cleaning ultraviolet lamps, is the use of a "caution" notice. However, in many instances such caution notices are either ignored, accidentally removed, or otherwise not effective, resulting in a user looking directly at an energized lamp, without adequate eye protection.
Further, while there is a certain degree of control in large industrial settings, such as ensuring automatic turn off of the lamps when a door is open, these turn offs are not implemented in the smaller sized settings. Particularly, in the smaller installations no access door provided, due in part to size constraints. In view of the foregoing, if there is an increase in the number of sterilization units used in residential or smaller settings, there will likely be a corresponding increase in the number of users forgetting or ignoring instructions to de-energize the lamps and/or otherwise not following the proper precautions resulting in an increase in injuries.
Thus, there has not been a wide use of ultraviolet sterilization equipment in residential or smaller installations where de-energizing of the lamps is not ensured. This is in part due to manufacturers' concerns of being liable for injuries sustained by a person misusing the sterilization equipment. The above factors result in an undesirable situation where bacteria and other micro-organisms, which would otherwise be destroyed, through application of ultraviolet rays are recirculated through an air heating and cooling systems thereby increasing the spread of viruses, bacteria, etc. in these settings.
Therefore, it has been deemed desirable to develop an ultraviolet sterilization unit for use in forced air heating and cooling systems which ensures the turning off/de-energizing of an ultraviolet lamp prior to exposing the lamp to the view of a user. Further, the ultraviolet sterilization unit should be compact and easy to insert within the air heating and cooling ducts thereby encouraging those with limited mechanical capabilities to install the unit. Still further, the ultraviolet sterilization unit should be configured for use with multiple lamps and should ensure the turning off of all lamps in the multiple lamp unit when any one of the lamps is removed and/or exposed to human view.